Automotive vehicles (as, for example, automobiles, trucks and/or buses) have been, in the generally recent past, designed with greater sophistication as regards, for example, vehicular braking systems as well as other apparatus for physically assisting the vehicle operator to operate the vehicle and/or informing or warning the vehicle operator of the occurrance of a particular condition which condition may or may not be undesirable.
For all practical purposes at least an overwhelming majority of automotive vehicles are now constructed as to include what is commonly referred to as a "power brake" system or a "power assist" brake system. Usually, such vehicular brake systems are comprised of, for example, a two chamber housing with a pressure responsive movable wall or diaphragm means therein effectively forming a common wall as generally between such two chambers. One of the chambers is, in the main, at ambient pressure while the second of such chambers is effective for having, for example, an engine generated vacuum applied thereto. When the vehicular operator actuates the operator brake pedal, such motion is converted to a valving function whereby an increasing (depending upon the degree of brake pedal application) magnitude of vacuum is made to exist in such second chamber causing, in turn, the movement of the pressure responsive wall means which, in turn, causes the movement of a hydraulic piston which serves to displace and pressurize related brake fluid means resulting in the application or energization of the vehicular wheel braking means.
In such "power assist" brake systems, the vacuum to the said second chamber (through the related valving means) may be supplied generally directly by conduit means operatively interconnecting such said second chamber and the engine intake manifold or it may be supplied through conduit means having a vacuum tank, accumulator or reservoir in series circuit therewith. Such vacuum tanks, accumulators or reservoirs are, in effect, a safety measure assuring that if the engine should for some reason stall or cease operation while the vehicle is in motion, there will still be a minimum amount of vacuum sufficient to stop the vehicle. Most often, such vacuum reservoirs are employed as on trucks and buses since the braking systems thereof require relatively large amounts of vacuum which exceed the amount that the engine could instantaneously deliver.
In the recent past automobile engines have been made much smaller some having 1.5 liter, or even less, displacement. One of the consequences of such is that the reduced "breathing" capacity of the engine also limits the volumetric capacity of the engine vacuum developed thereby. It has been discovered that at times the magnitude of the available vacuum for vehicle braking has diminished to a degree which might become unsafe especially if the vehicle is traveling at a fairly fast speed and under relatively high engine load.
Accordingly, the invention herein disclosed is primarily, although not exclusively, directed to a means whereby, upon the vacuum available for vehicle braking (for any reason) decreases in magnitude to a preselected value, a signal is generated for alerting the vehicle operator. However, as will become more apparent, even though the problems described arose in a particular field or art, the invention is not so limited and may be employed in differing fields or arts.